Phytonutritional Composition and Antioxidant Properties of Southern African, Purple-Fleshed Sweet Potato (Ipomoea batatas (L.) Lam.) Storage Roots

Purple sweet potatoes (Ipomoea batatas (L.) genotype) in Southern Africa have a phytonutritional composition and antioxidant properties that can increase incomes and improve nutrition. This study compared the phytonutrient composition and antioxidant properties of four purple-colour sweet potato genotypes (local Purple-purple, ‘2019-1-1’, and USA genotypes, ‘08-21P’ and ‘16-283P’). These purple sweet potato genotypes were characterised by UPLC/QTOF/MS and 16 phenolic compounds were identified. Purple-purple (very dark purple) showed the highest concentration of cyanidins and peonidin derivatives. Chlorogenic acid derivatives were highest in the genotype ‘16-283P’. ‘Puple-purple’ and ‘16-283P’ displayed the strongest antioxidant power and scavenging activities. Diaffeoylquinic acid isomer 1 was identified as the marker candidate for distinguishing the four purple sweet potato genotypes. Southern Africa’s highest-protein sweet potato genotypes are Purple-purple (28.81 g/100 g) and ‘08-21 P’ (24.31 g/100 g). A 13.65 g portion of ‘2019-1-1′ would meet the Recommended Dietary Allowance (RDA) for iron for men, while 25.59 g would meet the RDA for children, and 30.72 g would meet the RDA for women. The sweet potato root of genotype ‘2019-1-1′ provides 31.43 g of Zn per day for children and 22.86 g for adults. The roots of local cultivar Purple-purple can be used as functional food ingredients.


Introduction
Sweet potatoes are dicotyledonous plants (Ipomoea batatas (L.) Lam) of the Convolvulaceae family [1].It is one of the most widely grown crops in the world and is considered a food security crop.Sweet potato is among several crops that have been used successfully for biofortification to reduce hidden hunger, specifically, a micronutrient deficiency aligned with a shortage of vitamin A, by breeding orange-fleshed cultivars rich in carotenoids [2].Sweet potatoes are key staple food in South America, the Caribbean, Asia, and Africa and are a good source of calcium, iron, zinc, vitamins A and C, magnesium, phosphorus, and potassium [3].The Food and Agriculture Organisation (FAO) stated that 109 nations produced sweet potatoes in 2019.China produced 46.6 million metric tons of sweet potatoes in 2022 [4].The production of sweet potatoes increased by 1.5% in 2022 after two years of decline in Africa [5].Malawi, Nigeria, Tanzania, Uganda, Ethiopia, Angola, Rwanda, Madagascar, Burundi, and Kenya are 10 of the world's top 20 sweet potato-producing countries (Food and Agriculture Organization) [6].Sweet potatoes are commonly cultivated for the consumption of their storage roots of various pleasant colours from cream/white, purple, and yellow to orange [7].There are 131 million tons of sweet potatoes grown worldwide each year, and it ranks third in importance after potatoes [8].The varieties of staple roots in Sub-Saharan Africa are white-or cream-fleshed, distinguished by having high starch content [9].
In South Africa, the Agricultural Research Council programme includes the breeding and commercialisation of sweet potatoes, developing cultivars with a tolerance to major diseases and a better yield and root quality traits, i.e., high levels of anthocyanins [10].The South African Agricultural Research Council has released 33 genotypes thus far, with some, like 'Ribbok', 'Bosbok', and 'Blesbok', being commercialised.'Blesbok', a cultivar with purple skin, is known for its high yield and low dry matter content [11,12].Ndou and Monate have a high yield and high dry matter content, with cream flesh and cream skin [13].Additionally, there are orange-fleshed cultivars with a high β-carotene content, such as Bophelo and Khumo.Among the more recent developments are breeding lines FS10-25 and FS10-21, which produce cream-fleshed storage roots with purple skin known for their excellent storability and wilt tolerance.
Recently, breeders have shown interest in purple-fleshed sweet potato cultivars, as highlighted by Parker et al. [14].The main aim of breeding is to produce cultivars with high levels of anthocyanin and antioxidant capacity [15].Purple sweet potatoes are rich in anthocyanins, starch, polysaccharides, caffeoylquinic acid derivatives, vitamins, and minerals [16].Additionally, anthocyanins have antimutagenic, hepato-protective, antihypertensive, antihyperglycemic, antimicrobial, anti-inflammatory, and anti-obesity properties [17].According to Ghasemzadeh et al. [18] and Dwiyanti et al. [19], compared to the anthocyanin found in red cabbage, elderberries, blueberries, and red corn, the pigment anthocyanin in purple sweet potatoes has a higher stability.Sweet potatoes with purple flesh are rich in cyanidin and peonidin glycosides, which acylate their sophorose through the presence of phydroxybenzoyl, caffeoyl, and feruloyl moieties [20].However, the content of anthocyanin, caffeoylquinic acid derivatives, protein, fibre, Fe, Zn, and the antioxidant activity of purple varieties grown in South Africa are unknown.The objective of the present study was to investigate phytonutritional composition, including mineral elements Fe and Zn, total and individual phenolic compounds, and the antioxidant activities of the purple-colour flesh sweet potato roots found in the Southern African region-the Agricultural Research Council breeding lines '2019-1-1' (purple skin with purple, cream-ring flesh), the locally collected genotype Purple-purple (dark purple skin with very dark purple flesh), and two imported cultivars from the USA ('08-21P' and '16-283P').

Total Marketable Yield and Morphological Assessment
After harvest, the total marketable yield was determined (Scale Model Alpha 2 LCD, Jiangsu, China) and the results were expressed as kg/20 plants.On the day of harvesting, ten storage roots from each genotype were chosen for morphological assessment.
Diameter (cm), length (cm), and cortex thickness (mm) were measured using a calliper.The shape, pigmentation, and distribution of pigmentation of the storage roots were recorded based on International Potato Centre (CIP) sweet potato descriptors (Huamari, 1992).The pigmentation and distribution of pigmentation of the storage roots were recorded as explained by Selokela et al. [21].

Chemical Analysis
A set of 50 storage roots of each genotype, devoid of deterioration or damage, was selected randomly and pooled, and from those, 10 subsamples were taken for chemical analysis.These were washed with tap water [23] and transported to the Fruit and Vegetable Laboratory at the Tshwane University of Technology, in Pretoria West.Thereafter, the roots were chopped and freeze-dried (VirTis Sp Scientific, Model # 2kBTES-55, Gardiner, NY, USA) at −47 to −53 °C for 72 h and ground into fine powder, then stored at 4 °C until use.

Chemicals
The chemicals and standards mentioned below were purchased from Lasec SA (Pty) Ltd. in Midrand, Gauteng, South Africa.

Total Marketable Yield and Morphological Assessment
After harvest, the total marketable yield was determined (Scale Model Alpha 2 LCD, Jiangsu, China) and the results were expressed as kg/20 plants.On the day of harvesting, ten storage roots from each genotype were chosen for morphological assessment.
Diameter (cm), length (cm), and cortex thickness (mm) were measured using a calliper.The shape, pigmentation, and distribution of pigmentation of the storage roots were recorded based on International Potato Centre (CIP) sweet potato descriptors (Huamari, 1992).The pigmentation and distribution of pigmentation of the storage roots were recorded as explained by Selokela et al. [21].

Chemical Analysis
A set of 50 storage roots of each genotype, devoid of deterioration or damage, was selected randomly and pooled, and from those, 10 subsamples were taken for chemical analysis.These were washed with tap water [23] and transported to the Fruit and Vegetable Laboratory at the Tshwane University of Technology, in Pretoria West.Thereafter, the roots were chopped and freeze-dried (VirTis Sp Scientific, Model # 2kBTES-55, Gardiner, NY, USA) at −47 to −53 • C for 72 h and ground into fine powder, then stored at 4 • C until use.

Chemicals
The chemicals and standards mentioned below were purchased from Lasec SA (Pty) Ltd. in Midrand, Gauteng, South Africa.

Total Phenolic Content (TPC)
The TPC was determined from purple-fleshed storage roots using the procedure explained by Hong et al. [24].Each sample weighing 10 mg was extracted with 10 mL of 80% methanol using magnetic stirring (Edison, H4000-HSB, Sayreville NJ 08872, USA).The TPC was calculated using the standard curve generated with chlorogenic acid, which had concentrations ranging from 0-100 ppm, and the measurements were expressed in milligrams per gram of chlorogenic acid equivalent.

Ferric Reducing Antioxidant Power (FRAP)
The FRAP value was established according to the protocol described by Selokela et al. [21].The absorbance was then measured at 593 nm using a spectrophotometer.A standard curve was created with standards ranging from 0 to 700 concentrations, and the results were expressed as mM TEAC/g.The equation for the standard curve was Y = 0.0005x + 0.1216, with an R 2 value of 0.98.

2,2-Diphenyl-1-picrylhydrazyl (DPPH) Assay
The DPPH scavenging ability was used to measure inhibiting activity with some minor changes, following the method described by Suárez et al. [25].The inhibiting activity of the storage roots was measured by the decrease in absorbance in the methanol solution of DPPH.The IC 50 (mg/mL) was calculated using the concentration versus inhibition % graph.2.4.5.2,2 ′ -Azino-bis (3-Ethylbenzothiazoline-6-sulfonic Acid) Scavenging Activity ABTS scavenging activity was carried out, following the method explained by Seke et al. [26] A measurement was made of the decline in absorbance at 734 nm.A graph of the percentage of inhibition versus the concentration was used to determine the IC 50 (mg/mL).

Mineral Composition
Fe, Zn, and K were determined using the digest solution in an aliquot and (ICP-OES) inductively coupled plasma optical emission spectrophotometer [(Agilent 725 Series) Santa Clara, CA, USA] device.Mineral content was expressed on a dry weight basis [21].

Quantification of Phenolic Compounds Using UPLC-QTOF/MS
The identification and quantification of predominant phenolic acids and flavonoids were achieved using a UPLC-QTOF/MS system (Waters, Milford, MA, USA) equipped with a Quadrupole 120 time-of-flight (QTOF) mass spectrometer, following the method described by Managa et al. [27] without any modifications.The calibration curve set up using a chlorogenic acid standard was used to quantitatively and semi-quantitatively measure all identified compounds.The content of phenolic compounds in the study is expressed as mg/kg.Data were processed using TargetLynx software as previously reported [28].The data generated by the UPLC-Q-TOF/MS and HPLC-DAD (individual anthocyanins) analysis were analysed using principal component analysis (PCA) and Projections to Latent Structures-Discriminant Analysis (PLS-DA) approaches to identify the differences between the phenolic profiles of the different genotypes of the sweet potatoes' roots.The regression equation, and retention times' limit of detection (LOD) and limit of quantification (LOQ), for anthocyanins and phenolic compounds are shown in Supplementary Table S1.

Proximate Composition
Analyses were conducted to determine protein, total dietary fibre, and fat, following the procedures outlined by the Association of Official Analytical Chemists [29].

Statistical Analysis
Variance was analysed on all data collected and means separation using Tukey's truly significant difference (Tukey's HSD).All the data collected in this study were analysed using statistical package design Gen stat 18.1.The data were obtained during the 2022 and 2023 growing seasons.The results of the two harvests were compared, and as the data did not differ, it was pooled together and subjected to analysis of variance (ANOVA) using GenStat 11.1.

Morphological Characteristics of Five Purple-Fleshed Genotypes
The storage roots of different coloured sweet potato genotypes differ greatly from one another in terms of their morphological characteristics (Table 1).Most of the roots were long, elliptical, obovate, ovate, or round.The size and quantity of sweet potato storage roots depend on the root system and other characteristics of the plant, which are influenced by the environmental conditions of the growing areas [30].Additionally, several factors can affect sweet potato morphology, including the season, agricultural practices, and the characteristics of the plant itself [31].The skin colour of the storage roots of '2019-1-1 ′ , '08-21P', '16-283P', and Purple-purple ranged from light purple to dark purple.The flesh of '2019-1-1' had purple inner rings surrounded by cream outer rings.The roots of '08-21P' were violet and pink-cream, and the roots of '16-283P' were dark purple with a slight ring.Only the roots of Purple-purple showed a very dark purple flesh colour (Figure 1).The surface defects of sweet potato roots ranged from being absent to long thick veins, severe cracks, and alligator-like skin.Furthermore, the yield of these four genotypes varied significantly during the growing seasons (Table 2).Harvested yields for these four purple sweet potatoes were as follows: '08-21P' produced 20.64 kg/20 plants; '2019-1-1' (5.45 kg/20 plants); Purple-purple (15.48 kg/20 plants); and '16-283P' (7.56 kg/20 plants).The ARC-developed genotype '2019-1-1' showed lower yields than the locally found Purple-purple.The root lengths of these four purple sweet potatoes were 21.80 cm, 20.40 cm, 17.00 cm, and 16.85 cm in the '08-21P', Purple-purple, '16-283P', and '2019-1-1 ′ genotypes, respectively (Table 2).The diameter of the roots varied among the four genotypes.The highest root diameter was observed in '2019-1-1' (5.48), followed by '08-21P' (5.07), Purple-purple (4.26 cm), and '16-283P' (4.18 cm).The Purple-purple (3.9 cm) and '08-21P' (3.40 cm) genotypes showed the largest cortex diameters and were followed by '16-283P' (2.80 cm) and '2019-1-1' (1.16 cm) as shown in Table 2. Sweet potato storage roots are reported to vary in length and diameter [3;303].The farmer's choice of sweet potato variety depends on the independent variable weight, since it directly affects crop yield [32].Furthermore, sweet potato morphology is crucial when screening new genotypes because consumers may reject roots with undesirable traits [32].Data present mean and standard deviation (n = 10) and Tukey's HSD of four purple-fleshed sweet potato storage root genotypes.Significant variances are indicated by distinct letters within the same column at (p < 0.001).

Colour Properties
Food colour is a crucial quality parameter for sweet potatoes.Table 3 displays the colour attributes of four storage roots of purple-fleshed sweet potatoes.Purple-purple had the lowest L* value (deep purple) and exhibited a darker colour.Hence, the brightness or darkness of the flesh colour of the roots is determined by the L* value.Light purple flesh colours were seen with a higher L* value, while dark purple flesh colours were seen with a lower L* value [17].It is also important to note that the proportion of lightness (L*) and colour coordinates a* and b* influence flesh colour.Meanwhile, a positive a* colour coordinate relates to a higher red-colour intensity, while a positive b* colour coordinate relates to a higher yellow intensity.The genotype '2019-1-1' exhibited a higher L* value when compared to Purple-purple and the two genotypes from the USA.However, its a* colour coordinate was similar to that of '16-283P' but lower than both '08-21P' and Purple-purple.The chroma value of genotype '2019-1-1' was higher than '08-21P' but lower than '16-283P' and similar to Purple-purple, indicating a purple and cream flesh colour.In addition, colour values are very important to breeders to breed new varieties (Nakagawa et al. [33]).Genotypes with a deep purple colour are appropriate as constituents for flour colourants and snacks [17].Sweet potatoes are purple because of anthocyanins.Sweet potatoes contain peonidin and cyanidin, which are the most abundant anthocyanins.The flesh appears red-purple when peonidin levels exceed 1, while it appears purple-blue or grey when cyanidin levels dominate.The genotype '08-21P' consistently had the highest value for the a* colour coordinate in both seasons, while the genotypes '2019-1-1 ′ and '16-283P' had the lowest.Data present mean and standard deviation (n = 3) and Tukey's HSD.Significant variances are indicated by distinct letters within the same column at (p < 0.001).

The Metabolomic and Chemometric Profiles of Five Purple Sweet Potatoes Available in the Sub-Saharan African Region
Using UPLC-Q-TOF/MS results, unsupervised PCA analysis showed which sweet potato genotypes have the most and least phenolic compounds.Two-dimensional scatter plots of PC1 versus PC2 explained 98.9% of the variance (82.1% and 16.8%, respectively) (Figure 2A).The metabolites of the four genotypes helped to separate the four genotypes' purple sweet potatoes into three distinct clusters, with their corresponding loadings provided in Supplementary Table S2.The loading plot (Figure 2B) revealed that the larger the distance between its point and its original point, the more a compound contributes to the total variation.Thus, the compound dicaffeoylquinic acid isomer 1 (diCQA 1), which was loaded negatively (r= −0.97) on PC1 and was the most distant from the original point, helped to separate the 16-283p genotype from the rest.Chlorogenic acid (components coefficient r = −0.75)and 5CQA (r = −0.61)were loaded negatively on PC2 and separated the genotypes Purple-purple and 16-283 from the other two genotypes.PLS-DA was utilised in this study to classify different genotypes based on their 16 metabolites.In total, 98.9% of the variation in bioactive compounds can be explained by the first two principal components (PC1 73.3% and PC2 25.6%) (Figure 2A).Three major clusters were identified based on the PLS-DA plot. Figure 2B shows the loading of different phenolic metabolites on PC1 and PC2, and the loading of the compounds is given in Supplementary Table S3.The compound diCQA 1 was loaded positively (r = 0.5) on PC2 and was distant from the original point, while 5CQA (r = 6.0) and chlorogenic acid (r = 0.63) were also loaded positively on PC2 and were able to separate the Purple-purple and 16-283 genotypes from the others.In addition to generating more accurate predictions, PLS-DA produces more meaningful models [49].The PLS-DA model showed a high prediction level (Q2 = 0.97) as well as a high goodness-of-fit level (R 2 = 0.82).
original point, while 5CQA (r= 6.0) and chlorogenic acid (r= 0.63) were also loaded positively on PC2 and were able to separate the Purple-purple and 16-283 genotypes from the others.In addition to generating more accurate predictions, PLS-DA produces more meaningful models [49].The PLS-DA model showed a high prediction level (Q2 = 0.97) as well as a high goodness-of-fit level (R 2 = 0.82).
A variable importance in projection (VIP) score was used to evaluate the contribution of each metabolite to the separation of groups (Figure 2E).VIP scores are determined by summing the weighted PLS regression coefficients and the squares of the PLS loadings.Only the top metabolites with the highest VIP scores are considered for interpreting the results [50].Among the top six metabolites with VIP scores >1 are chlorogenic acid 5CQA, chlorogenic acid 3CQA, and dicaffeoylquinic acid isomer 1diCQA.Diaffeoylquinic acid isomer 1 diCQA allowed us to distinguish the two groups.

Antioxidant Activities
Based on a genotype comparison, the Purple-purple and '16-283P' genotypes had the highest antioxidant activities (FRAP, ABTS, and DPPH) (Table 7).In general, sweet potato roots with a purple colour had a higher antioxidant activity, which confirmed Ji et al.'s [51] findings.
The discrepancy in antioxidant activities and total phenolic content may be explained by the amount of rainfall that each harvest season received.In the presence of water stress, secondary metabolites can be produced to protect against oxidative stress [52].As a result of accumulating polyphenols and acylated anthocyanins with high antioxidant activity from the very beginning of their growth, sweet potato roots are protected from biotic and abiotic stress [53].A variable importance in projection (VIP) score was used to evaluate the contribution of each metabolite to the separation of groups (Figure 2E).VIP scores are determined by summing the weighted PLS regression coefficients and the squares of the PLS loadings.Only the top metabolites with the highest VIP scores are considered for interpreting the results [50].Among the top six metabolites with VIP scores >1 are chlorogenic acid 5CQA, chlorogenic acid 3CQA, and dicaffeoylquinic acid isomer 1diCQA.Diaffeoylquinic acid isomer 1 diCQA allowed us to distinguish the two groups.

Antioxidant Activities
Based on a genotype comparison, the Purple-purple and '16-283P' genotypes had the highest antioxidant activities (FRAP, ABTS, and DPPH) (Table 7).In general, sweet potato roots with a purple colour had a higher antioxidant activity, which confirmed Ji et al.'s [51] findings.The discrepancy in antioxidant activities and total phenolic content may be explained by the amount of rainfall that each harvest season received.In the presence of water stress, secondary metabolites can be produced to protect against oxidative stress [52].As a result of accumulating polyphenols and acylated anthocyanins with high antioxidant activity from the very beginning of their growth, sweet potato roots are protected from biotic and abiotic stress [53].
Data present mean and standard deviation (n = 3) and Tukey's HSD.Significant variances are indicated by distinct letters within the same column at (p < 0.001).

Protein, Fat, Dietary Fibre
Table 8 shows significant differences in protein, fat, and dietary fibre composition between coloured sweet potato genotypes.The protein content of the sweet potato genotypes varied significantly, with the genotype Purple-purple exhibiting the highest value (28.81 ± 1.34) and the genotype 16-283P exhibiting the least value (19.12 ± 0.62) in Table 8.In addition, the total protein values (on a dry basis) were higher than those documented in the literature for sweet potatoes.Cartier et al. [58] reported a protein content of 4.07 ± 0.21-6.20 ± 0.17 g/100 g and Rodrigues et al. [59] (5.82 ± 1.43 g/100 g).Proteins play a vital role in biological activities like development and repair, depending on their bioaccessibility after digestion [58].According to the current study, Purple-purple (28.81 g/100 g) and '08-21 P' (24.31 g/100 g) are the sweet potato genotypes with the highest protein content for human nutrition in Sub-Saharan Africa.Therefore, sweet potato storage roots should be promoted and encouraged to maintain a balanced diet.A 100 g portion of Purple-purple would contribute 17.7% of a 65 kg adult male's recommended daily protein allowance based on 0.8 g per day multiplied by weight.The protein content of the sweet potato roots of genotypes Purple-purple and '08-21P' showed a higher composition than the Ethiopian genotypes G1 (Ukrewe × Ejumula-10) (7.43%), G5 (Ukrewe × Ogansagan-5) (7.29%), G6 (Resisto × Ejumula-7) (6.99%), G8 (Resisto × PIPI-2) (7.08%), and G17 (Resisto × Ogansagen-16) (6.44%), and G18 (Resisto × Ogansagen-16) (7.84%) showed the highest protein content [60].The fat content of the storage roots was the highest in 2019-1-1 (0.83 ± 0.01 g/100 g), with genotype Purple-purple showing the lowest content of 0.47 ± 0.02 g/100 g (Table 8).On the contrary, Mitiku and Teka, [61] reported that sweet potatoes contained 1.25-1.52g/100 g of fat and Hossain et al. [30] reported ranges of between 0.73 ± 0.05 and 2.41 ± 0.02 g/100 g, which were significantly higher than the results from our current study.In Brazil, a purple genotype has been reported with a lower fat content between 0.42 ± 0.04 g/100 g and 0.39 ± 0.03 g/100 g [59].The differences can be attributed to climatic growing conditions, soil type, and location differences.Considering the recommended daily allowance for fats, a 100 g portion of genotype '2019-1-1 ′ on a fresh weight basis would contribute 1% to the daily allowance for a 65 kg adult male.Genotype '2019-1-1 ′ , based on its high fat content, might be marketed as a food flavouring.

Fe, Zn and K Content
Fe and Zn deficiencies are estimated to be 5 and 40% in Sub-Saharan Africa, respectively [63].Sweet potato roots of the genotypes '2019-1-1' and Purple-purple (Table 9) measured similar Fe levels as the Ethiopian genotypes G8 (2.55 mg per 100 g), G17 (2.16 mg per 100 g), and G19 (2.20 mg per 100 g).Iron (Fe) content ranged from 1.85 to 2.77 mg/100 g in purple sweet potato genotypes, higher than those in Benin (0.53 to 0.73 mg/100 g) [64] and orange-and-cream-flesh genotypes from South Africa (0.73 to 1.26 mg/100 g) [12].The significant differences in Fe content may be attributed to genotype variation, as all samples were collected from the same experimental farm.Fe deficiency is linked to common micronutrient deficits such as anaemia, particularly in children, as well as vitamin A insufficiency.A 13.65 g portion of 2019-1-1 on a fresh weight basis would meet the Recommended Dietary Allowance (RDA) for iron for men, while 25.59 g for children and 30.72 g for women would meet their respective RDAs.The zinc (Zn) content ranged between 0.95 and 1.42 mg/100 g, with genotype '2019-1-1 ′ (1.42 ± 0.20 mg/100 g), '16-283P' (1.32 ± 0.10 mg/100 g), and Purple-purple (1.3 ± 0.13 mg/100 g) (Table 9) exhibiting the highest composition.Nevertheless, Sanoussi et al. [64] reported a lower Zn content (0.27 mg/100 g).The trace element Zn is essential for protein synthesis, immunity, and gene expression [65].The sweet potato root of genotype 2019-1-1 will meet the daily recommended allowance of Zn for children at 31.43 g and 22.86 g for adults.Potassium (K) content ranged from 13.3 to 22.2 mg/100 g, with cultivar 2019-1-1 having the highest K content at 22.20 mg/100 g.Hossain et al. [30] reported a range between 8.8 and 12.4 mg/100 g, which is lower than the genotypes studied here.Sanoussi et al. [64] and Senthilkumar et al. [66] reported higher levels (308.67 to 328.67 mg/100 g).K plays a role in controlling water balance, neurotransmission, and heart rate [64].However, the 100 g sweet potato 2019-1-1 studied would contribute only 0.21% of the recommended daily allowance for adults and 0.24% of the recommended daily allowance for children.Data present mean and standard deviation (n = 3) and Tukey's HSD.Significant variances are indicated by distinct letters within a same column at (p < 0.001).Key: Fe: Iron, K: Potassium, Zn: Zinc.

Figure 1 .
Figure 1.Shape and size of roots and distribution of anthocyanin in four purple-fleshed genotypes.

Figure 1 .
Figure 1.Shape and size of roots and distribution of anthocyanin in four purple-fleshed genotypes.

Figure 2 .
Figure 2. (A) An unsupervised PCA score plot of phenolic metabolites generated by UPLC-QTOF/MS analysis showing the separation of three clusters.(B) Loading of phenolic metabolites in the PCA score plot.(C) A PLS-DA score plot showing four sweet potato cultivars clustered into three groups.(D) PLS-DA score plots loaded with different phenolic compounds detected by UPLC-QTOF-MS showing two clustered groups, (E).Metabolites are assigned VIP scores in PLS-DA.Variable importance is determined by the score they receive from low to high.Each metabolite's relative concentration is shown in the coloured boxes on the right.Low blue levels indicate low levels, while high red levels indicate high levels.(F) Heat map.In the map, the various phenolic compounds found in different sweet potato cultivars are coloured according to their concentration.The rows represent phenolic compounds, and the columns represent the sweet potato genotype.The colours red and blue indicate high and low levels, respectively.

Table 1 .
Morphological characteristics of four genotypes of purple-fleshed sweet potato storage roots.

Table 2 .
Yield, length, diameter, and cortex of the four different genotypes of purple sweet potato storage roots.

Table 3 .
Flesh colour values of four genotypes of purple-fleshed sweet potato storage roots.

Table 4 .
Total phenolic content of four genotypes of purple-fleshed sweet potato storage roots.

Table 5 .
Identification and quantification of cinnamic acids and derivatives and flavonoid composition of purple-coloured sweet potato (Ipomoea batatas L.) genotypes found in Sub-Saharan Africa by UPLC-QTOF/MS.

Table 6 .
Identification and quantification of anthocyanin composition of purple-coloured sweet potato (Ipomoea batatas L.) genotypes found in Sub-Saharan Africa by UPLC-QTOF/MS.

Table 7 .
Antioxidant activities of four different genotypes of purple-fleshed sweet potato storage roots.

Table 8 .
Protein, fat, and dietary fibre composition of four different, purple-fleshed sweet potato storage root genotypes (DW).

Table 9 .
Iron, zinc, and potassium composition of four different, purple-fleshed sweet potato storage root genotypes.